Parallel motion device



Patented Sept. 19, 1939 UNITED STATES PATENT OFFICE Application August 15,

1 Claim.

1938, Serial No. 224,971

(Granted under the act of March 3, 18.83, as amended April 30, 1928;, 370 G. 757) This invention relates to, parallel motion devices for use on drawing or chart boards, and it has for .its principal object the provision of a simple and compact device of the character described which will reach any part of a drawing or chart without projecting over the edges of the board.

With these and other objects in view, as well as other advantages that may be incident to the use of the improvements, the invention consists in the parts and combinations thereof hereinafter set forth and claimed, with the understanding that the several necessary elements constituting the same may be varied in proportion and arrangement without departing from the nature and scope of the invention, as defined in the appended claim.

In order to make the invention more clearly understood, there are shown in the accompanying drawing, means for carrying the invention into practical use, without limiting the improvements in their useful application to the particular construction, which, for the purpose of explanation, have been made the subject of illustration.

In the accompanying drawing:

Fig. 1 is a plan view of a parallel motion device constructed in accordance with the invention;

Fig. 2 is a vertical, longitudinal, sectional view taken on line 2-2 of Fig. 1;

Fig. 3 is a vertical, transverse, sectional View taken on line 33 of Fig. 1; and

Fig. 4 is a diagrammatic plan view on a smaller scale showing the device mounted on a drawing or chart board.

Referring to the drawing, a parallel motion device constructed in accordance with the invention is shown as comprising a pair of bars l0 which are pivotally mounted in spaced parallel relation on a drawing or chart board H by means of pivot pins l2 engageable with inwardly extending ears |3 formed on the bars ||J near adjacent ends thereof. A link I4 is pivotally connected to the opposite ends of the bars ID by 45 means of pins I5 which are disposed the same distance apart as the pins l2 and at the same distance therefrom so that the bars ID will move in unison and in parallelism when swung about their pivots I2.

The bars ID are each formed with a vertically extending bracket |6 having a bearing I! at its upper end in which a stud shaft I8 is fixed. Rotatably mounted on each of the stud shafts IB is a spool or reel I9 on which a flexible metallic tape 20 is fixed at one end and around which the tape is wound for several turns. From the reel 9 each of the tapes passes around an idler pulley or drum 2| which is fixed to a stud shaft 22 rotatably mounted in a bearing 23 provided on a bracket 24 formed on. the bar l0. After leaving 5 the drums 2| the tapes 20 each pass beneath its reel H! and through guides 25 formed on the bars l0 and are pivotally connected at their free ends by a bar on instrument support 26 by pivot pins 21. The distance between the pins 21 is equal to 10 that between the pins l5 so as to maintain the tapes parallel.

The tapes 2!] are preferably curved in crosssection so as to be relatively inflexible or rigid in a transverse direction, but are flattened out 15 when wound upon the reels i9 and when passing around the idler pulleys 2| where they are held in close contact therewith by a plurality of circumferentially spaced retaining rollers 28 journalled in extensions 29 of the brackets 24. The 20 idler pulleys 2| are preferably provided with a plurality of circumferential projections or teeth 36 for engagement with openings 3| formed in 1 the tape 20, the rollers 28 being grooved to permit of the passage of the projections 30. Slip- 25 page between the pulleys 2| and the tapes is thus prevented. The idler pulleys are tied together so as to rotate in unison when the tapes are drawn out, by means of a shaft 32 which is rotatably mounted in a bearing 33 carried by a pedestal 34 30 fixed tothe drawing board endwise movement of the shaft 32 being prevented by collars 35 carried thereby for engagement with the ends of the bearing 33. The outer ends of the shaft 32 are connected with the shafts 22 by means of 35 universal joints 36 (Fig. 3), which are disposed directly above the pivot pins l2 so that the pulleys 2| may rotate freely and in unison when the bars l0 are turned. Spiral springs 31 are fixed to the stud shafts l8 and to the inner face of the reels 40 I9 so as to oppose the rotation of the reels when the tapes 20 are drawn out and to maintain the tapes under tension.

From the foregoing it will be apparent that inasmuch as the idler pulleys 2| are tied together by means of the universal shaft 32 to rotate in unison, and by reason of the fact that the tapes 2|] cannot slip on the idler pulleys due to the sprocket connection therebetween, they must each move the same amounts when retracted or extended. Also, by reason of the described arrangement of links and pivots the parts will be maintained in parallelism when the device is swung about its pivot pins I2. As a result, an instrument 38, such as a square, straight ed'ge,

compass rose or the like carried by the link 26 may be moved to any position over the board and paper or chart placed thereon and still maintain the angular position to which it is initially adjusted. If desired, the instrument may be secured to the bar 26 by means of an angular adjustable clamp 39 having a Vernier attachment similar to those employed with the well known universal draftin machines.

It will be understood that the above description and accompanying drawing comprehend only the general and preferred embodiment of the invention and that various changes in construction, proportion and arrangement of the parts may be made within the scope of the appended claim without sacrificing any of the advantages of the invention.

The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

A parallel motion drafting device comprising a pair of spaced elongated brackets adapted to be pivotally mounted at adjacent ends to a chart board or the like, means pivotally connecting together the free ends of said brackets for maintaining them in parallelism when they are swung about their pivotal mountings, a reel rotatably mounted on each of said brackets, a toothed idler pulley rotatably mounted on each of said brackets in alinement with the associated reel, a transversely rigid metallic tape wound upon each of said reels and passing around said pulleys, said tapes having uniformly spaced openings therein through which the teeth of said idler pulleys are adapted to project, means pivotally connecting together the free ends of said tapes at the same distance apart as the free ends of said brackets for also maintaining said tapes in parallelism and for supporting a drafting or calculating instrument, means for yieldably opposing the rotation of said reels when said tapes are unwound therefrom to maintain said tapes under tension, and a shaft having a universal connection with each of said idler pulleys for effecting the rotation of said reels and pulleys in unison so as to maintain the unwound portions of said tapes at uniform lengths.

JERAULD WRIGHT. 

